Tenter device

ABSTRACT

A clip has a frame and a flapper. Two dry bearings are inserted into a hole formed in the flapper. Then an attaching shaft is inserted from one of the holes in the frame to the other through the dry bearings, so as to swingably attaching the flapper to the frame. DAIDAYNE DDK 01 of DAIDO METAL Corp. is used as the dry bearing. A first and a second clip covers are provided to cover the clips. Fresh air feeding pipes are connected to the first and second clip covers. Fresh air is fed from the fresh air feeding pipes toward the clips through air outlets provided in the first and second clip covers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tenter device used in a filmproduction apparatus for solution casting method.

2. Description Related to the Prior Art

To produce a polymer film having no unevenness of thickness and opticalproperties, a tenter device has clips for holding lateral edges of thefilm, and moves the clips which hold the film. The film is dried whilebeing transported. The clip is assembled such that a flapper isrotatably attached to a U-shaped frame through an attaching shaft anddry bearings. The flapper is biased to a holding position by own weight.When the flapper is at the holding position, the film is held between alower end surface of the flapper and a film holding surface of theframe. In addition, when an upper end surface of the flapper contacts aclip opener, the flapper is rotated to a retreat position where theholding of the film is released. The clip starts the holding of the filmat an entrance of the tenter device, and releases the holding at an exitof the tenter device. Tenter devices using this type of clips aredisclosed in Japanese Patent Laid-Open Publications No.11-77719 andNo.11-90943.

However, when this conventional tenter device is used for producingcellulose acylate film, although at the beginning a film having highretardation value and superior optical properties can be produced, aftera certain period of time, some clips start misholding of the filmbecause of poor smoothness of the swing of the flapper. When a part ofthe film is misheld by the clip, there occurs unevenness of thickness oroptical properties of the dried film.

In addition, there becomes a possibility to break the soft film formedby solution casting, when springs or the like are used for biasing theswing of the flapper so that the flapper is swung to the holdingposition regardless of lack of the smoothness of swing.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a tenter device used ina film producing apparatus for solution casting method, in whichsmoothness of swing of a clip does not become lower even after a certainperiod of time has passed.

In keen examination, the inventor found that TPP (triphenyl phosphate)contained in a film as a plasticizer is vaporized from the film when thefilm is dried, the vaporized TPP is condensed as dew on a dry bearing ofthe clip, and then the condensed TPP and dust from the dry bearing arebound together to be a crystallized mass. The dust is generated by slidefriction between the dry bearing and an attaching shaft. The slidesmoothness of the dry bearing becomes reduced by the existence of thecrystal. Accordingly, the clip cannot be moved to a film holdingposition by biasing of its own weight.

In order to achieve the object and other objects, a tenter device of thepresent invention has clips for clipping both lateral edges of a film,and moves the clips for transporting the film while dry air is fed froma dry air blower onto the film for drying the film. The clip comprises amain body having a film holding surface on which the lateral edge of thefilm is positioned, a holding lever swingable between a holding positionfor holding the lateral edge of the film on the film holding surface anda retreat position for releasing the holding of the film, an attachingshaft for attaching the holding lever to the main body, and at least onedry bearing supporting the attaching shaft. The dry bearing is formed ofmaterial, which generates lower dust by wearing compared to materialcontaining lead, and is self-lubricating.

It is preferable that the dry bearing is formed ofpolytetrafluoroethylene and solid lubricant. It is preferable that thetenter device further includes a clip cover for covering a moving pathof the clip in the state that the holding lever is at the holdingposition and a fresh air blower for feeding fresh air into inside of theclip cover so as to prevent the dry air outside of the clip cover fromblowing into the inside of the clip cover. It is preferable that thefilm is a cellulose acylate film.

According to the tenter device of the present invention, since the drybearing is formed of material which generates lower dust by wearingcompared to material containing lead and is self-lubricating, thesmoothness of swing of the flapper hardly becomes lower.

In addition, in case the dry bearing is formed ofpolytetrafluoroethylene and solid lubricant, the dry bearing is notdeteriorated by vaporized contents of the film. Therefore, thesmoothness of swing of the flapper does not becomer lower.

In addition, when the tenter device further includes the clip cover, forcovering the moving path of the clip in the state that the holding leveris at the holding position, and the fresh air blower for feeding freshair into inside of the clip cover so as to prevent the dry air outsideof the clip cover from blowing into inside of the clip cover, it isprevented that the vaporized content of the film in the dry air and dustparticles on the dry bearing generated by the wearing are bound togetherto form a mass. Therefore, the smoothness of swing of the flapper doesnot become lower.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomeeasily understood by one of ordinary skill in the art when the followingdetailed description would be read in connection with the accompanyingdrawings.

FIG. 1 is a top plan view of a tenter device of the present invention;

FIG. 2 is a perspective view of a clip in the tenter device;

FIG. 3 is an exploded perspective view of the clip in FIG. 2;

FIG. 4 is a cross-sectional view of the tenter device, in which the clipdoes not hold a film;

FIG. 5 is a cross-sectional view of the tenter device, in which the clipholds the film;

FIG. 6 is a cross-sectional view of the clip, a first clip cover and afresh air feeding pipe;

FIG. 7 is a schematic view of the tenter device, showing the first andsecond clip covers and a TPP removing unit;

FIG. 8 is a schematic view of a dope producing apparatus; and

FIG. 9 is a schematic view of an apparatus for producing a film bysolution casting.

PREFERRED EMBODIMENTS OF THE INVENTION

As shown in FIG. 1, a tenter device 2 is used for drying a wet film 3peeled from a casting belt 113 (refer to FIG. 9), with transporting thewet film 3 in a film feeding direction A and stretching the wet film 3in a width direction B of the wet film 3. The tenter device 2 comprisesa first rail 5, a second rail 6, and a first and a second chains(endless chains) 7, 8 which are guided by the rails 5,6. The tenterdevice 2 has three areas, which are a first drying area 2 a, a seconddrying area 2 b and a third drying area 2 c arranged in this order froma tenter device inlet 16. In each drying areas 2 a–2 c, dry air is fedfrom a dry air circulation unit 60 (refer to FIG. 7) toward the wet film3. Accordingly, the wet film 3 being transported in the drying areas 2a, 2 b, 2 c becomes dried. Although the tenter device 2 has three areasin this embodiment, the number of the areas is not limited to thisembodiment.

To the first and second chains 7,8, plural clips 10 are attached atcertain intervals. The clips 10 hold lateral edges of the wet film 3 andmove along the rails 5,6. While the movement of the clips 10, the wetfilm 3 is stretched in the width direction B. Note that in thisembodiment, when the width of the wet film 3 before being stretched was100%, that of the stretched film 3 was 103%. However, the stretchingratio is not limited to this embodiment.

The first and second chains 7,8 are hanged on drive sprockets 11,12 anddriven sprockets 13,14, respectively. The drive sprockets 11,12 areprovided in a side of a tenter device outlet 17, and rotated by drivers(not shown). The driven sprockets 13,14 are provided in a side of thetenter device inlet 16. At the tenter device inlet 16, clip openers21,22 for opening the clip 10 to a retreat position are attached to thefirst and second rails 5,6, respectively. At the tenter device outlet17, also clip openers 23,24 are attached to the first and second rails5,6, respectively.

As shown in FIG. 2 and FIG. 3, the clip 10 comprises a U-shaped frame(clip main body) 31, a flapper (holding lever) 32 and a rail attachingportion 33. In the frame 31, two flapper attaching portions 34 areformed for attaching the flapper 32 to the frame 31. In the flapperattaching portion 34, there are a hole 34 a for insertion of anattachment shaft 35, and a hole 34 b for insertion of a fixing pin 36.The fixing pin 36 is for fixing the attachment shaft 35 inserted intothe hole 34 a. The hole 34 b for the fixing pin 36 penetrates theflapper attaching portion 34 in up-and-down direction. In the attachmentshaft 35, holes 35 a for insertion of the fixing pins 36 are formed atpositions corresponding to the holes 34 b of the flapper attachingportion 34.

The flapper 32 comprises a contact head 32 a for contacting to the clipopeners 21–24, a film holder 32 b for holding the wet film 3 on a filmholding surface 31 a of the frame 31, a rotational shaft 32 c, and ahole 32 d penetrating the rotational shaft 32 c for insertion of drybearings 37 from ends thereof. Therefore, the dry bearing 37 is formedfrom materials having press-fittability (for example plastics). In thisembodiment, DAIDAYNE DDK 01 of DAIDO METAL Corp. is used as the drybearing 37.

An assemble method of the clip 10 is now described. At first, the drybearings 37 are inserted into the both ends of the hole 32 d of theflapper 32. Then the attachment shaft 35 is inserted from the one of theholes 34 a to the other through the dry bearings 37, and the two offixing pin 36 are inserted into the holes 34 b, 35 a. Accordingly, theattachment shaft 35 is fixed to the flapper attaching portion 34 withinability to rotate, and the flapper 32 is rotatably attached to theframe 31. While the flapper 32 rotating, the dry bearings 37 slide onthe attachment shaft 35.

As shown in FIG. 4 and FIG. 5, the rail attaching portion 33 is attachedto the first chain 7 or the second chain 8. The flapper 32 rotatesbetween a film holding position(holding position), where the flapper isat right angle to the film holding surface 31 a, and the retreatposition, where the flapper is at a slant to the film holding surface 31a because the contact head 32 a contacts one of the clip openers 21–24.The flapper 32 is biased to the holding position by an own weight. At afilm holding start position (start position) PA (refer to FIG. 1), thewet film 3 is held between the film holding surface 31 a and the filmholder 32 b.

The rail attaching portion 33 comprises an attachment frame 41 and guiderollers 42–44. To the attachment frame 41, one of the first and secondchains 7,8 is attached. The guide rollers 42–44 are rotated withcontacting the driven sprocket 13,14 and the first and second rails 5,6.Therefore, the clip 10 does not drop off from the sprockets 13,14 andthe rails 5,6.

The clip opener 21/22 contacts the contact head 32 a of the flapper 32of the clip 10 right before the clip 10 reaches to the start positionPA, so that the flapper 32 is rotated from the holding position to theretreat position. Then the lateral side of the wet film 3 is positionedon the film holding surface 31 a of the frame 31. When the clip 10passes the start position PA, the contact head 32 a is apart from theclip opener 21/22 so that the flapper 32 is rotated from the retreatposition to the holding position. Accordingly, the lateral side of thewet film 3 is held between the film holding surface 31 a and the filmholder 32 b. In the same way, the clip opener 23/24 rotates the clip 10from the holding position to the retreat position at a film holdingrelease position (release position) PB. Then the holding of the lateralside of the wet film 3 is released, and the wet film 3 goes outside ofthe tenter device 2 from the tenter device outlet 17. The wet film 3 outfrom the tenter device outlet 17 is fed to an edge slitting device 142as a film 141 (refer to FIG. 9). Note that the clip openers 21–24 arepreferably formed from resin, such that the friction between the clipopener and the contact head 32 a of the flapper 32 is kept low. As theresin, nylon, Delrin (registered trademark) and the like are preferablyused.

As shown in FIG. 6 and FIG. 7, first and second clip covers 51,52 areprovided respectively above the first and second rails 5,6, so as tocover the clip 10. The first and second clip covers 51,52 extend betweenthe start position PA and the release position PB in the tenter device2. The second clip cover 52 has a same structure of the first clip cover51, therefore only the first clip cover 51 is described later in detail.

As shown in FIG. 6, the first clip cover 51 covers the frame 31 and theflapper 32 of the clip 10 moving along the first rail 5. To the firstclip cover 51, fresh air feeding pipes 55 are connected. The connectedposition of each of the air feeding pipes 55 corresponds to the each ofdrying areas 2 a–c. The fresh air feeding pipe 55 is for feeding freshair toward the clip 10, mainly the flapper 32. Flow volume of the freshair is controlled by a valve 62 connected to the air feeding pipe 55.

The fresh air fed from the fresh air feeding pipe 55 blows toward theflapper 32 through an air outlet 56 provided in the first clip cover 51.The air outlet 56 extends along the first clip cover 51 in the filmfeeding direction A. Since the fresh air is contained inside the firstclip cover 51 so that the pressure inside the first clip cover 51becomes higher than that outside thereof, it is prevented that the dryair for drying the wet film 3 contacts the clip 10.

To the first and second clip covers 51,52 respectively, an exhaust cover57 is connected. The fresh air inside the clip covers 51,52 is send to acooling device (not shown) through the exhaust cover 57, and the cooledfresh air is send to the dry air circulation unit 60. In the dry aircirculation unit 60, a temperature of the fresh air is regulated to apredetermined range by a heat exchanger (not shown). The regulated airis fed toward the each of drying areas 2 a–2 c as the dry air.

As shown in FIG. 7, the dry air in the each of drying areas 2 a–2 c issend to a TPP removing unit 65 connected to the respective drying areas2 a–2 c. In the drying areas 2 a–2 c, TPP (triphenyl phosphate)contained in the wet film 3 as a plasticizer is vaporized. Therefore,the dry air contains the vaporized TPP. The TPP removing unit 65 removesthe TPP contained in the dry air sent from the drying areas 2 a–2 c. Thedry air in which the TPP is removed is fed to the fresh air feeding pipe55 connected to the TPP removing unit 65. In the fresh air feeding pipe55, outside air is taken from outside the pipe 55 by opening a valve(not shown), and the outside air and the dry air from the TPP removingunit 65 flow together as the fresh air.

As described above, since the fresh air blows toward the flapper 32 fromthe air outlet 56, it is prevented that the TPP is attached to theflapper 32, the attachment shaft 35 and the dry bearing 37. In addition,since the first and second covers 51,52 cover the frame 31 and theflapper 32 of the clip 10, it is further prevented that the dry aircontaining the TPP contacts the clip 10.

A method of producing the wet film 3 is described in followings.However, a method and an apparatus for the production as described beloware examples, and the present invention is not restricted to thedescribed below.

A cellulose acylate is used as a polymer in this embodiment, and it ispreferable that a triacetyl cellulose (TAC) is used as the celluloseacylate. The TAC made from either of linter and pulp cotton is usable inthe embodiment, but the one from the linter cotton is preferably used.In addition, the cellulose acylate, whose degree of the substitutionsatisfies all of following formulae (I)–(III), is more preferable. Inthese formulae, A is a degree of substitution of the hydrogen atom ofthe hydroxyl group to the acetyl group, and B is a degree ofsubstitution of the hydrogen group to the acyl group having 3–22 carbonatoms. Preferably, at least 90 mass % of the cellulose acylate particleshas diameter from 0.1 mm to 4 mm.2.5≦A+B≦3.0   (I)0≦A≦3.0   (II)0≦B≦2.9   (III)

Solvent compounds for preparing the dope are aromatic hydrocarbon (forexample, benzene toluene and the like), halogenated hydrocarbons (forexample, dichloromethane, chloroform, chlorobenzene and the like),alcohols (for example methanol, ethanol, n-propanol, n-butanol,diethylene glycol and the like), ketones (for example acetone,methylethyl ketone and the like), esters (for example, methylacetate,ethylacetate, propylacetate and the like), ethers (for exampletetrahydrofuran, methylcellosolve and the like) and the like. Note thatthe dope means a polymer solution or a dispersed solution obtained bydissolving or dispersing the polymer in the solvent.

The preferable solvent compounds are the halogenated hydrocarbons having1 to 7 carbon atoms, and dichloromethane is especially preferable. Inview of physical properties such as optical properties, a solubility, apeelability from a support, a mechanical strength of the film and thelike, it is preferable to use at least one sorts of the alcohols having1 to 5 carbon atoms with dichloromethane. The content of the alcohols ispreferably in the range of 2 mass % to 25 mass %, and especially in therange of 5 mass % to 20 mass % to total solvent compounds in thesolvent. As concrete example of the alcohols, there are methanol,ethanol, n-propanol, isopropanol, n-butanol, and the like. It ispreferable to use methanol, ethanol, n-butanol or a mixture thereof.

Recently, in order to reduce the influence on the environment, thesolvent containing no dichloromethane is proposed. In this case, thesolvent contains ethers with 4 to 12 carbon atoms, ketones with 3 to 12carbon atoms, esters with 3 to 12 carbon atom, or a mixture of them. Theethers, ketones, esthers may have a cyclic structure. At least onesolvent compound having at least two functional groups thereof (—O—,—CO—, —COO—) may be contained in the organic solvent. Note that theorganic solvent compound may have other functional group such asalcoholic hydroxy group.

The cellulose acylate is described in detail in Japanese patentlaid-open publication No. 2005-104148, and the description of thisapplication can be applied to the present invention. Further, as thesolvent of cellulose acylate and other additives, this applicationdiscloses plasticizers, deteoriation inhibitor, optical anisotropycontrolling agent, dye, matting agent, release agent and releasepromoter in detail.

[Method of Producing the Dope]

First, the dope is made from above raw materials. A dope producingapparatus 70, which is described in FIG. 8, comprises a solvent tank 71for containing a solvent, a dissolving tank 73 for mixing the solventand TAC, a hopper 74 for supplying the TAC and a additive tank 75 forstoring the additives. The dope producing apparatus 70 further comprisesa heater 86 for heating a swelling liquid described below, a temperatureregulator 87 for regulating the temperature of the heated swellingliquid, filtration devices 88 and 95, a flushing device 91 for adjustingthe concentration of the dope. In addition, the dope producing apparatus70 comprises a recovering device 92 for recovering the solvent and areproducing device 93 for reproducing the recovered solvent. The dopeproducing apparatus 70 is connected to a film producing apparatus 100through a reserve tank 90.

In this embodiment, the dope is made in the dope producing apparatus 70by a method in the followings. At first, the solvent is transported fromthe solvent tank 71 to the dissolving tank 73 by opening a valve 72.Next, the measured volume of TAC is transported from the hopper 74 tothe dissolving tank 73, and the required volume of the additive liquidis transported from the additive tank 75 to the dissolving tank 73 byopening a valve 76.

There are other methods except for additives to be transported as thesolution. For example, the additives can be directly transported intothe dissolving tank 73 if additives are in liquid state at the normaltemperature. The additives can be transported into the dissolving tank73 by a hopper if the additive is in solid state. If plural kinds ofadditives are used, it can be that a solution dissolving all of them isstored in the additive tank 75, and it can be that each of solutionsincluding single additive is stored in a separate additive tank andtransported into the dissolving tank 73 through each corresponding pipe.

In the above embodiment, the order in which materials transported intothe dissolving tank 73 is the solvent, the TAC and additives. However,the order is not restricted to this way. For example, after the TAC istransported into the dissolving tank 73, intended volume of the solventcan be transported. In addition, additives is not required to bepreliminarily stored in the dissolving tank 73, but can be mixed into amixture of the TAC and the solvent at the after process.

The dissolving tank 73 comprises a jacket 77 which covers the outside ofthe tank 73 as shown in FIG. 8, and a first stirrer 79 rotated by amotor 78. Further, preferably the dissolving tank 73 comprises a secondstirrer 81 rotated by a motor 80. Note that preferably the first stirrer79 has a anchor blade and the second stirrer 81 is an eccentric stirrerof dissolver type. Temperature inside the dissolving tank 73 isregulated by a heating medium flowing in the jacket 77. The temperatureis preferably in the range of −10° C. to 55° C. By individuallycontrolling the rotation of the first stirrer 17 and the second stirrer81, a swelling liquid 82 in which the TAC swells in the solvent is made.

Next, the swelling liquid 82 is transported to the heater 86 by a pump85. Preferably, the heater 86 has a jacketed pipe and a pressure devicefor pressurizing inside the pipe. In the heater 86, solid contents inthe swelling liquid 82 are dissolved in the solvent by being heated orby being heated and pressurized. Note that preferably temperature of theswelling liquid 82 is heated in a range of 50° C. to 120° C.(hereinafter this method is called the heating dissolution method). Aknown cooling dissolution method, in which the temperature of theswelling liquid 82 is cooled in a range of −100° C. to −30° C., is alsoapplicable to obtain the dope. The heating and cooling dissolutionmethods are selected according to the properties of the TAC for thedissolving. A temperature of the dope is controlled to approximatelyroom temperature by the temperature regulator 87, and then the dope isfiltrated by the filtration device 88 so that impurities are removedfrom the dope. Preferably the average hole diameter of a filter in thefiltration device 88 is less than 100 μm. Preferably flow rate of thefiltration is equal to or more than 50 liter/hour. The dope after thefiltration is stored in the reserve tank 90 through a valve 89.

The method stated above, that once the swelling liquid 82 is preparedand then making the dope from the swelling liquid 82, possibly needshigh product cost, because longer manufacturing time is required to makethe dope having higher concentration of the TAC. To reduce the cost, itis preferable that a dope having the TAC in lower concentration than adesired concentration is prepared, and then a concentration process isperformed, in which the concentration of the TAC is elevated to thedesired concentration. For the concentration process being applied tothe dope, the dope filtrated in the filtration device 88 is transportedinto the flushing device 91 through the valve 89, so that a part ofsolvent in the dope is vaporized in the flushing device 91. The solventvapor is condensed into liquid by a condenser (not shown). The liquid isrecovered by the recovering device 92 and reproduced by the reproductiondevice 93 to be reused as the solvent for preparing the dope. Thisrecycling process has an advantage in terms of cost.

The condensed dope 96 is drawn from the flushing device 91 out by a pump94. Further, preferably air bubbles generated in the dope 96 areremoved. Any known methods to remove the air bubble are applicable (forexample, ultrasonic irradiation method). Next, the dope 96 istransported to the filtration device 35 in which impurities in the dope96 are removed. Note that the temperature of the dope 96 when beingapplied these processes is preferable in a range of 0° C. to 200° C. Thedope 96 is transported to and stored in the reserve tank 90. And thedope in the reserve tank 90 is transported into the film producingapparatus 100.

Preferably, the primary dope and the additive liquid (for example theUV-absorbing liquid) in transporting are mixed by an inline mixer (forexample a static mixer). It is preferable that plural inline mixers eachof which has a structure for the mixing different from the other mixerare serially connected.

Preferably, at least either the static mixer or a sulzer mixer is usedas the inline mixer. When the static mixer is used, the mixer haspreferably 6 to 90 elements, more preferably 6 to 60 elements.

In case that both the static mixer and the sulzer mixer are equipped asthe inline mixer, the sulzer mixer is preferably disposed at a positionupstream from the static mixer. Further, a distance between the sulzermixer and an additive liquid inlet is preferably in a range of 5 mm to150 mm, more preferably in a range of 5 mm to 15 mm. In addition, anupstream side edge of an element of the sulzer mixer is preferablydisposed near an inner surface of the pipe in which the primary dopeflows.

Preferably, a first filtration device for filtrating the primary dope isdisposed at a position upstream from the inline mixer, and the additivesare mixed into the dope filtrated by the first filtration device. Inaddition, it is preferable that a second filtration device forfiltrating the dope is disposed at a position downstream from the inlinemixer, and the dope mixed by the inline mixer is filtrated by the secondfiltration device.

Preferably, the embodiment is performed with satisfying followingconditions.

(1) 1≦V1/V2≦5 when V1 is defined as a flow velocity of the additiveliquid and V2 is defined as the flow velocity of the raw materialliquid.

(2) a ratio of the additive liquid within the dope is in a range of 0.1%to 50% by rate of flow volume.

(3) 1000≦N2/N1≦100000, and at 20° C., 5000 cP≦N1≦500000 cP and 0.1cP≦N2≦100 cP when N1 is defined as viscosity of the additive liquid andN2 is defined as viscosity of the primary dope.

(4) The shear speed of the dope is in a range of 0.1 (1/s) to 30 (1/s).

(5) The polymer is the cellulose acylate.

(6) The additive liquid is the solution containing the main solvent ofthe polymer solution.

(7) The additive liquid is the solution containing the main solvent ofthe polymer solution, and the composition of the additive liquid isdifferent from the dope.

(8) The additive liquid is the solution including the main solvent ofthe polymer solution, and further including at least one kind of UVabsorbing agent.

(9) The additive liquid is the solution including the main solvent ofthe polymer solution, and being made from dispersed particles of atleast one kind of inorganic or organic material.

(10) The additive liquid is the solution including the main solvent ofthe polymer solution, and further including at least one kind of peelingpromoter.

(11) The additive liquid is the solution including the main solvent ofthe polymer solution, and further including at least one kind of poorsolvent.

The TAC concentration is preferably in a range of 5 mass % to 40 mass %,especially in a range of 15 mass % to 30 mass %, particularly in a rangeof 17 mass % to 25 mass %. A concentration of the additives (mainlycomposed of the plasticizer) is preferably in the range of 1 mass % to20 mass % to total solid components in the dope. Note that methods foradding and dissolving raw materials and additives of a dope, filteringthe dope, removing bubbles, and other methods in the solution castingmethod for producing the TAC film are explained in Japanese PatentLaid-open publication No. 2005-104148. The content of this publicationcan be applied to the present invention.

[Solution Casting Method]

A method for producing film from the dope 96 is described later.However, the present invention is not restricted to be applied to theapparatus in FIG. 9. The film producing apparatus 100 comprises afiltration device 104, a casting die 110, a casting belt 113 supportedby rollers 111, 112, and the tenter device 2. The film producingapparatus 100 further comprises the edge slitting device 142, a dryingchamber 145, a cooling chamber 147 and a winding chamber 150.

A stirrer 102 rotated by a motor 101 is provided in the reserve tank 90.The reserve tank 90 is connected to the casting die 110 through a pump103 and the filtration device 104.

As the material of the casting die 110, a precipitation hardenedstainless or a stainless having double-phase structure is preferablyused. The material has coefficient of thermal expansion of at most2×10⁻⁵ (° C.⁻¹), the almost same anti-corrosion properties as SUS316 inexamination of corrosion in electrolyte aqua solution. Further, when thematerial was dipped in a mixture liquid of dichloromethane, methanol andwater, pitting (holes) were not formed on the gas-liquid interface. Thesurface roughness of a contacting surface of the casting die 110 to thedope is at most 1 μm, straightness is at most 1 μm/m in each direction,and the clearance of the slit is automatically controlled in the rangeof 0.5 mm to 3.5 mm. An end of the contacting portion of each lip to thedope was processed so as to have a chamfered radius at most 50 μmthrough the slit. In the die, the shear speed is preferably in the rangeof 1 (1/sec) to 5000 (1/sec).

Preferably, a width of the casting die 110 is about 1.0 to 2.0 timeslarger than a width of the product film. Preferably, a device forregulating the temperature of the casting die is attached to the castingdie 110 such that the casting is performed with the temperature of thecasting die being kept in a predetermined range. Further, preferably thecasting die 110 is coathanger type, in which bolts (heat bolts) forautomatically adjusting the thickness of the film are provided withpredetermined intervals in the width direction of the casting die 110.The heat bolts preferably set a casting profile according to the flowvolume from the pump 103 by a preset program. The casting profile can bealso adjusted by a feedback control based on a measured value from athickness measurement device (not shown) provided in the film productiondevice 100 (for example, an infrared thickness measurement device).Thus, in the film except of the edge portions, the difference of thethickness at any two points apart is preferably at most 1 μm, andfurther the difference of the minimal thickness value and the maximalthickness value in the widthwise direction is preferably at most 3 μm,especially at most 2 μm. The variation of the lip clearance ispreferably in a range of ±50 μm.

Further, lip ends are provided with a hardened layer. In order toprovide the hardened layer, there are methods of ceramic coating, hardchrome plating, nitriding treatment and the like. If the ceramics isused as the hardened layer, the grind was possible, the porosity becomeslower, and was not friable and the good corrosion resistance. Further,as the preferable ceramics, there was no adhesive property to the dope.Concretely, as the ceramics, there are tungsten carbide, Al₂O₃, TiN,Cr₂O₃ and the like, and especially tungsten carbide. Note in the presentinvention the hardened layer is preferably formed by a tungsten carbidecoating in a spraying method.

A device for supplying a solvent (not shown) is preferably provided onthe both edges of a die slit in order to prevent the discharged dopepartially dried to be a solid. Preferably, the solvent to which the dopewas dissoluble (for example, a mixture solvent whose composition isdichloromethane 86.5 mass.pct, acetone 13 mass.pct, n-butanol 0.5mass.pct) is supplied to each bead edge and the air-liquid interface ofthe slit. The pump for supplying the dope preferably has a pulsation atmost 5%.

Below the casting die 110, there is the belt 113 supported by therollers 111, 112. The belt 113 moves endlessly and circulatory inaccordance with a rotation of the rollers 111 and 112 by a drivingdevice (not shown). The moving speed of the belt 113, namely a castingspeed is preferably in the range of 10 m/min to 200 m/min. Furthermore,the rollers 111,112 are connected to a heat transfer medium circulator114 for keeping a surface temperature of the belt 113 to a predeterminedvalue. In each roller 111,112, there is a heat transfer passage in whicha heat transfer medium of the predetermined temperature is fed, so as tokeep the temperature of the rollers 111,112 to the predetermined value.Thus the surface temperature of the belt 113 is controlled to thepredetermined value. Note that the surface temperature is preferablyfrom −20° C. to 40° C.

The rollers 111, 112 are also usable as the support itself. In thiscase, preferably the rollers rotates with a high accuracy that thedeviation of the rotational velocity is at most 0.2%. Preferably asurface roughness of a contacting surface of each of the rollers 111,112 was at most 0.01 μm. The surface of the each rollers 111, 112 areprocessed by the hard chrome plating so as to have the enough hardnessand durability. Note that the support (the belt 113 or the roller 111,112) preferably had minimum defect on the surface thereof. Preferably,the number of pinholes whose diameter is at least 30 μm is zero, that ofthe pinholes whose diameter is at least 10 μm and at most 30 μm is atmost 1 per 1 m², and that of the pinholes whose diameter is less than 10μm is at most 2 per 1 m².

The casting die 110, the belt 113 and the like are contained in acasting chamber 115. In the casting chamber 115, a temperature regulator116 to regulate the temperature inside the chamber and a first condenser117 to condense a vaporized organic solvent is provided. A recoveringdevice 118 to recover the condensed organic solvent is provided outsideof the casting chamber 115. Preferably, a decompression chamber 120 isprovided in the casting chamber 115 in order to control a pressure atthe backside of a casting bead formed between the casting die 110 andthe belt 113.

Air blowers 121,122,123 for feeding a drying air onto the casting film119 is provided so that the organic solvent may evaporate from thecasting film 79. Positions of the air blowers are an upper and upstreamside, an upper and downstream side, and a lower side of the belt 113.However, the positions are not restricted in this figure. The surfacecondition of the film sometimes changes when the drying air is appliedonto the casting film 119 just after the formation thereof. In order toreduce the change of the surface condition, a wind shielding device 124is preferably provided.

An air blower 131 is provided in an interval section 130, and a crasher143 is provided in an edge slitting device 142 in a position downstreamfrom the tenter device 2. The crasher 143 crushes cut both edges of thefilm 141 into fragments (tips).

There are plural rollers 144 in the drying chamber 145. A recoveringdevice 146 for adsorbing and recovering the solvent vapor is connectedto the drying chamber 145. In FIG. 9, a cooling chamber 147 is providedin a position downstream from the drying chamber 145. A moisture controlchamber (not shown) may be provided between the drying chamber 145 andthe cooling chamber 147. In a position downstream from the coolingchamber 147, a compulsory neutralization device (neutralization bar) 148is provided such that the charged voltage on the film 141 may be in therange of −3 kV to +3 kV. However, the position of the neutralizationdevice 148 is not restricted in FIG. 9. Further, a knurling roller 149for providing a knurling with an embossing processing in the both edgesof the film 141 is provided in a position downstream from the compulsoryneutralization device 148. And, a winding roller 151 to wind the film141 and a press roller 152 to control the tension on the film in windingare provided inside the winding chamber 150.

An example of the method for producing the film in the film producingapparatus 100 will be described in the followings. The dope 96 isconsistently uniformed by being stirred with the stirrer 112. Theadditives (plasticizer, UV-absorbing agent and the like) can be mixed inthe dope 96 while the stirring.

The dope 96 is transported by the pump 103 to the filtration device 104in which the dope 96 is filtrated, and is cast from the casting die 110to the belt 113. A tension on the belt 113 is preferably regulated in arange 10⁴N/m to 10⁵N/m by the drive of two rollers 111,112. Thedifference of the relative speed of the rollers 111,112 and the belt 113is preferably at most 0.01 m/min. Further, the fluctuation of thevelocity of the belt 113 is preferably at most 0.5%. The length of filmmeandering in width direction generated by one rotation is preferably atmost 1.5 mm. The rotation is preferably regulated by feedback from adetecting device (not shown) which detects the positions of both edgesof the belt 113, in order to reduce the film meandering. Further,preferably the positional fluctuation in horizontal directions of thelips and the belt 113 just below the casting die 110, which is generatedin the rotation of the roller 111 is regulated to at most 200 μm. Inaddition, the temperature in the casting chamber 115 is preferably inthe range of −10° C. to 57° C. The solvent vapor from inside the castingchamber 115 is recovered by the recovering device 78, and is reproducedfor being reused as the solvent for preparing the dope.

The casting die 110 casts the casting dope on the belt 113 to form thecasting film 119, while the casting dope form the bead above the belt113. Note that the temperature of the casting dope is preferably from−10° C. to 57° C. Further, in order to stabilize the formation of thebead, the decompression chamber 120 is preferably provided to control apressure on a rear side of the bead. Preferably, the pressure on therear side of the bead is decompressed in the range of −10 Pa to −1500 Pafrom the pressure of a front side of the bead. Further, preferably thetemperature inside the chamber 120 is regulated by a jacket attached tothe chamber 120 so as to keep the predetermined temperature. Preferablyan suctioning device (not shown) is provided at the edge portions of thecasting die 110 to keep the desired form of the casting bead. Preferablyvolume of the suction is in a range of 1 L/min to 100 L/min.

After having a self-supporting property, the casting film 119 is peeledas a wet film 3 from the belt 113 with support of a peel roller 125. Atthat time, the content of the remaining solvent is preferably in a rangeof 20 mass % to 250 mass % to total solid components in the film.Thereafter, the wet film 3 is transported to the tenter device 2 throughthe interval section 130 provided with plural rollers. In the intervalsection 130, a drying air at a predetermined temperature is fed from theair blower 131 such that the drying of the wet film 3 may proceed. Thetemperature of the drying air is preferably in the range of 20° C. to250° C.

The wet film 3 is dried while transported in the tenter device 2, withportions thereof are held by clips. In the tenter device 2, the wet film3 is stretched in the width direction B (see FIG. 1). The wet film 3 ispreferably stretched in the range of 100.5% to 300% at least whetherwidth or casting direction in whether the interval section 130 or thetenter device 2.

The wet film 3 becomes the film 141 containing a predetermined contentof the solvent in the tenter device 2. Then the film 141 is transportedinto the edge slitting device 142 for slitting off both edge portions ofthe film 141. The slit edge portions are conveyed to the crusher 143with use of a cutter blower (not shown). The crusher 143 crushes theboth edge portions into tips, which are reused for preparation of thedope in view of the cost. Note that the slitting off the both edgeportions of the film may be omitted. However, it is preferable to slitthem off somewhere between the casting of the dope and the winding thefilm.

The film 141 is transported into the drying chamber 145 so as to bedried further. The temperature in the drying chamber 141 is notrestricted especially. The drying of the film 141 in the drying chamber145 is made with wrapping around the pass roller 144 so as to evaporatethe solvent. The solvent vapor is adsorbed and recovered by therecovering device 146. The air from which the solvent vapor is removedis sent as the drying air again. Note that the drying chamber 145 ispreferably partitioned into plural partitions so as to vary the dryingtemperature. Further, it is preferable to provide a pre-drying chamber(not shown) between the edge slitting device 142 and the drying chamber145 so as to make the pre-drying of the film 141. In this case, thedeformation of the film which is caused by the accelerate increase ofthe temperature of the film is prevented.

The film 141 is transported into the cooling chamber 147, and cooled toan approximately room temperature. Note that a moisture control chamber(not shown) may be provided between the drying chamber 145 and thecooling chamber 147. In the moisture control chamber, an air whosemoisture and temperature are controlled is fed toward the film 141. Thusa winding defect and a curl of the film are prevented when the film 141is wound.

In the solution casting method, the peeled film (polymer film) beforewound up is applied various processes including the drying process and aprocess of cutting side edge portions of the film. While being appliedthese processes, the polymer film is supported and fed by rollers. Asthe rollers, there are drive rollers and non-drive rollers. Thenon-drive roller is used for determining a feeding path of the polymerfilm and increasing a stability of feeding.

The drive roller is used for transmitting the driving force to thepolymer film so as to feed it downstream. As the drive roller, a suctionroller is usually used. While feeding of the film, different filmtensions may be required in the different processes, such as the castingprocess, the peeling process, the drying process and the windingprocess. In this case, the suction roller applies the driving force tothe film so as to change the film tension. The suction roller has aplurality of suction holes on a contact surface thereof so as to suckthe polymer film thereon while the feeding.

When the suction roller is used for feeding the film, since a complexpower whose direction cannot identify acts on the film, the film islikely to be deformed. Further, the film can be deformed by thedifference of the film tensions between upstream and downstream from thesuction roller. In addition, when the polymer film slips, contracts orbecomes deformed while contacting on edges of the suction holes,microscopic flaws are occurred on the film.

The surface of the driving roller used in the transporting process ishardened. The hardening may be performed by hard chrome plating,nitridation, quenching or the like. The degree of hardness is in a rangeof 500 to 2000, preferably in a range of 800 to 1200 in Vickershardness.

The drive roller is a suction roller 65 having a plurality of suctionholes 91 on its surface. The surface roughness Ry of the roller surface65 a is preferably in a range of 0.3 μm to 1.0 μm, particularly in arange of 0.5 μm to 0.8 μm. The value of the surface roughness Ry ismeasured in area of the roller surface without the suction hole. Adiameter of the suction hole is preferably in a range of 1 mm to 6 mm,particularly in a range of 2 mm to 4 mm. A width of chamfer of thesuction hole is preferably in a range of 2% to 20% in ratio to thediameter thereof.

While the suction roller is driven, it is preferable that a surfacetemperature thereof is controlled. For this purpose, at least one rollertemperature controller, which corresponds to the single suction roller,is preferably provided. It is preferable that the roller temperaturecontroller controls the surface temperature of the suction roller so asto be higher than temperature of the film immediately before contactingto the suction roller.

By the compulsory neutralization device (neutralization bar) 148,charged voltage on the film 141 is regulated in the range of −3 kV to +3kV in the transporting. In FIG. 9, the neutralization device 148 isdisposed in a position downstream from the cooling chamber 147. However,the position of the neutralization device 148 is not restricted in thisfigure. Further, it is preferable to provide a knurling roller 149 forproviding a knurling with an embossing processing. Note that theunevenness in the area in which the knurling is provided is preferablyin the range of 1 μm to 200 μm.

At last, the film 141 is wound around the winding shaft 151 in thewinding chamber 150. The winding is preferably made with applying apredetermined tension by the press roller 152, and it is preferable tochange the tension from a start to an end of the winding little bylittle. The length of the film 141 to be wound is preferably at least100 m, and a width thereof is preferably at least 600 mm, and especiallyfrom 1400 mm to 1800 mm. However, even if the width is more than 1800mm, the present invention is effective. Further, in the presentinvention, the thickness of the film to be produced is in the range of15 μm to 100 μm.

The solution casting method of the present invention may be a co-castingmethod in which a co-casting of two or more sorts of the dopes are madesuch that the dopes may form a multi-layer film, or a sequentiallycasting method in which two or more sorts of the dopes are sequentiallycast so as to form the multi-layer film. When the co-casting isperformed, a feed block may be attached to the casting die, or amulti-manifold type casting die may be used. A thickness of whetherupper or lowermost layer of the multi-layer casting film on the supportis preferably in the range of 0.5% to 30% to the total thickness of themulti-layer casting film. Furthermore, in the co-casting method, whenthe dopes are cast onto the support, it is preferable that the lowerviscosity dope may entirely cover over the higher viscosity dope.Furthermore, in the co-casing method, it is preferable that the innerdope is covered with dopes whose alcohol contents are larger in the beadfrom a die to the support.

Note that the laid-open publication No. 2005-104148 teaches in detailthe structure of the casting die and the support, drying conditions ineach processes (such as the co-casting, the peeling and the stretching),a handling method, a winding method after the correction of planarityand curling, a recovering method of the solvent, a recovering method offilm and the like. The description of the above publication may beapplied to the present invention.

[Characteristics, Measuring Method]

The laid-open publication No. 2005-104148 teaches the characteristicsand the measuring method of the cellulose acylate film, which may beapplied to the present invention.

[Surface Treatment]

It is preferable to make a surface treatment of at least one surface ofthe cellulose acylate film. Preferably, the surface treatment is atleast one of glow discharge treatment, atmospheric pressure plasmadischarge treatment, UV radiation treatment, corona discharge treatment,flame treatment, and acid or alkali treatment.

[Functional Layer]

A primary coating may be made over at least one surface of the celluloseacylate film. Further, it is preferable to provide other functionallayers for the cellulose acylate film as a film base so as to obtain afunctional material. The functional layers may be at least one ofantistatic agent, cured resin layer, antireflection layer, adhesivelayer for easy adhesion, antiglare layer and an optical compensationlayer.

Conditions and methods of performing a surface treatment and providing afunctional layer with several functions and characteristics aredescribed in the laid-open publication No. 2005-104148.

[Application]

The cellulose acylate film can be used as the protective film in apolarizing filter. To obtain a LCD, two polarizing filters, in each ofwhich the cellulose acylate film is adhered to a polarizer, are disposedso as to sandwich a liquid crystal layer. The laid-open publication No.2005-104148 discloses TN type, STN type, VA type, OCB type, reflectiontype, and other example in detail. To these types can be applied thefilm of the present invention. Further, the application teaches thecellulose acylate film provided with an optical anisotropic layer andthat provided with antireflective and antiglare functions. Furthermore,the application supposes to provide the cellulose acylate film withadequate optical functions, and thus a biaxial cellulose acylate film isobtained and used as the optical compensation film, which can be used asthe protective film in the polarizing filter simultaneously. Therestriction thereof described in the laid-open publication No.2005-104148 can be applied to the present invention.

In addition, a cellulose triacetate film (TAC film) having superioroptical characteristics can be obtained according to the presentinvention. The TAC film can be used as a base film of a photosensitivematerial or a protective film in a polarizing filter. The TAC film isalso used as an optical compensation film for widening a view angle of aliquid crystal display used for a TV monitor. In this case, preferablythe TAC film also has the function of the protective film in thepolarizing filter. Accordingly, the TAC film can be used for an IPS(In-Plane Switching) mode, an OCB (Optionally Compensatory Bend) mode, aVA (Vertically Aligned) mode and the like as well as for a conventionalTN (Twisted Nematic) mode.

EXAMPLE 1

As the dry bearing 37, it was prepared five materials, which were theDAIDAYNE DDK01 of DAIDO METAL Corp. used in the above embodiment, andsamples A to D. The DDK01 contains polytetrafluoroethylene (PTFE) andsolid lubricant. The sample A was DAIDAYNE DDU01 of DAIDO METAL Corp.,which is used for conventional dry bearing, including PTFE, lead andsolid lubricant. The sample B was DTK52 of DAIDO METAL Corp. includingpolyether ether ketone (PEEK). The sample C was AURAM (registeredtrademark) JCF3030 of MITSUI CHEMICALS, INC. including polyimide resin,carbon fiber and PTFE. The sample D was POLYPENCO (registered trademark)PEEK PK-450 of NIPPON POLYPENCO LIMITED including PEEK. Note that theDDK01 and the samples B to D are lead-free.

To evaluate dust generation from each of the materials, inner peripheralsurface of the dry bearing 37 of the each material was rubbed by a blackpaper, and an amount of dust on the black paper transferred from the drybearing 37 was measured. In addition, a durability test was performed toevaluate durability of the flapper 32 using the dry bearing 37 of theeach material. In the durability test, while the five clips 10incorporating the dry bearings 37 of the respective materials were in anoven heated to 150° C., the flapper 32 of the each clip 10 wascontinuously performed switching movement with weighted by a cylinder.The durability test was respectively performed in a fresh air atmosphereand a TPP atmosphere.

Results of the tests are shown in Table 1. In Table 1, the evaluation ofthe dust generation was made as follows:

“G” (Good) when the number of particles on the black paper was 0 to 2;

“P” (Pass) when the number of particles on the black paper was 3 to 9;

“R” (Reject) when the number of particles on the black paper was morethan 9.

In addition, the evaluation of the durability of the flapper was made asfollows:

“G” (Good) when the switching movement of the flapper 32 could becontinued at least 445000 times;

“P” (Pass) when the switching movement of the flapper 32 could becontinued 3001 to 444999 times;

“R” (Reject) when the switching movement of the flapper 32 could becontinued at most 3000 times.

TABLE 1 number of durability of flapper material of bearing particles infresh air in TPP DDK01 P G G sample A (DDU01) R G R sample B (DTK52) P GG sample C (JCF3030) P G P sample D (PK-450) P G G

When the DDK01, the sample B or the sample D was the material of the drybearing 37, the number of the particles was small (3 to 9), and theswitching movement of the flapper 32 could be continued at least 445000times both in the fresh air atmosphere and in the TPP atmosphere. Whenthe sample C was the material of the dry bearing 37, the number of theparticles was small (3 to 9), and the switching movement of the flapper32 could be continued 3001 to 444999 times in the TPP atmosphere, atleast 445000 times in the fresh air atmosphere. When the sample A wasthe material of the dry bearing 37, the number of the particles waslarge (at least 10), and the switching movement of the flapper 32 couldbe continued at most 3000 times in the TPP atmosphere, at least 445000times in the fresh air atmosphere. Note that the flapper 32 switchesapproximately 445000 times while the tenter device 2 is operated for ayear.

The results shows that the durability of the flapper 32 is improved whenthe dry bearing 37 is formed from materials which generate low dust andis lead-free. According to that, it is prevented that the wet film 3 ismisheld by defective movement of the flapper 32 caused by degradation ofthe dry bearing 37. In addition, when the clip 10 is operated in thefresh air atmosphere, the defective movement of the flapper 32 can beavoided more effectively, because it is prevented that the TPP isattached to the dry bearing 37 and which causes a binding between theparticles on the dry bearing 37 and the TPP to form mass.

EXAMPLE 2

Example of the film production of the present invention will beexplained. The composition of the polymer solution (the dope) used inthe process for producing the film is shown below.

[Composition]

Cellulose triacetate 100 mass. pct (substitution degree of acetyl groupwas 2.84, viscometric average degree of polymerization was 306, moisturecontent was 0.2 mass. %, viscosity of 6% by mass of dichloromethanesolution was 315 mPa · s, powder whose average of particle diameter was1.5 mm and standard deviation was 0.5 mm) Dichloromethane (firstsolvent) 320 mass. pct Methanol (second solvent) 83 mass. pct 1-butanol(third solvent) 3 mass. pct Plasticizer A (TPP) 7.6 mass. pctPlasticizer B (Diphenylphosphate) 3.8 mass. pct UV-absorbing agent a:0.7 mass. pct 2-(2′-hydroxy-3′,5′-di- tert-butylphenyl)benzotriazolUV-absorbing agent b: 0.3 mass. pct 2-(2′-hydroxy-3′,5′-di-tert-amylphenyl)-5-chlorobenzotriazole citric acid ester mixture: 0.006 mass.pct (citric acid, citric acid monoethylester, citric acid dietylester,citric acid trietylester) Particles: 0.05 mass. pct (silicon dioxidehaving a diameter of 15 nm, and Mohs hardness of approximate 7)

[Cellulose Triacetate]

Note that in the cellulose triacetate used in the example, content ofremaining acetic acid was less than 0.1 mass. %, content of Ca was 58ppm, content of Mg was 42 ppm, content of Fe was 0.5 ppm, content offree acetic acid was 40 ppm, and content of ion sulfate was 15 ppm.Degree of acetyl at 6^(th) position was 0.91 and that content was 32.5%of all acetyl and content extract from TAC by the acetone was 8 mass. %.A ratio of the average of molecular weight by weight to the average ofmolecular weight by number was 2.5. And yellow index of the obtained TACwas 1.7, haze was 0.08 and transparency was 93.5%. Tg(glass transitionpoint measured by DSC) was 160° C. and calorific value incrystallization was 6.4 J/g. This was called cotton material TAC inbelow description.

(1-1) Dope Preparation

The dope 96 was prepared by the dope producing apparatus 70 in FIG. 8.In the stainless dissolving tank 73 with volume 4000 L which has thestirring blade, the plural solvents were mixed and stirred so as to bethe mixture solvent. Note that each of those solvents has at most 0.5mass. % of moisture content. Flake powder of the TAC was gradually addedinto the dissolving tank 73 from the hopper 74. The Powder of the TACwas dispersed in the dissolving tank 13 for thirty minutes by the firststirrer 79 having the anchor blade and the second stirrer 81 which isthe eccentric stirrer of dissolver type. Temperature at start of thedispersion was 25° C., and that at the end of the dispersion was 48° C.Further, the prepared additive solution in the additive tank 75 wastransported into the dissolving tank 73 with volume regulated by thevalve 76. A weight of the content including the additive solution in thedissolving tank was 2000 kg. After finishing the dispersion of theadditive solution, the additive solution was further stirred for 100minutes by the first stirrer with predetermined rotation velocity, sothat the TAC flake was swollen to be the swelling liquid 82. Inside ofthe tank was pressurized to 0.12 MPa with nitrogen gas until theswelling. At this time the oxygen concentration inside the dissolvingtank 73 was kept less than 2 volt, therefore it was no possibility ofexplosion. And the content of the water was 0.3 mass. % in the swellingliquid.

(1-2) Dissolution and Filtration

The swelling liquid 82 was transported by the pump 85 from thedissolving tank 73 to the heater 86 having the jacketed pipe. Theswelling liquid was heated to 50° C. at first in the heater 86, and thenheated to 90° C. under the pressure of 2 MPa, so as to be dissolvedcompletely. At this time, the heating time was 15 minutes. Next, thetemperature of the dissolved solution became 36° C. in the temperatureregulator 87, and the solution was filtrated by the filtration device 88with a filter whose nominal pore diameter was 8 μm. Accordingly, a lowconcentration dope was obtained. At this time, a pressure at the primaryside was 1.5 MPa and a pressure at the secondary side was 1.2 MPa in thefiltration device 88. As the material of the filter, the housing and thepipe, which reach to high temperature, HASTELLOY alloy having excellentanti-corrosion property was used. In addition, the jacket in which theheat transfer medium passes through was attached to the filter, thehousing and the pipe.

(1-3) Condense, Filtration, Removal of Foams, Additives

The low concentration dope obtained in this way was flushed in theflashing device 91 under normal pressure and at the temperature of 80°C., and the vaporized solvent was condensed and recovered by thecondenser. According to that, the dope of desired concentration wasobtained. The condensed solvent was transported to the solvent tank 71after recovered for reuse in the recovering device 92 and reproduced inthe reproducing device 93. Distillation, dehydration and the like wasperformed in the recovering device 92 and the reproducing device 93. Astirrer having an anchor blade on a stirring shaft was provided insidethe flashing tank such that foams in the flashed dope were removed bystirring. The dope in the flash tank is at the temperature of 25° C.,and the average residence time of the dope in the tank was 50 minutes. Ashear viscosity of the dope measured at the temperature of 25° C. was450 Pa·s when a shear velocity was 10 (sec⁻¹).

After that, the dope was exposed to ultrasonic waves such that the foamsin the dope was removed. Next, the dope passed through the filtrationdevice 95 while being pressurized to 1.5 MPa by a pump. In thefiltration device 95, the dope firstly passed through a metal sinteredfilter whose nominal pore diameter is 10 μm and secondly passed througha sintered filter whose nominal pore diameter is also 10 μm. The primaryside pressures at each filtration were 1.5 MPa and 1.2 MPa, and thesecondary pressures at each filtration were 1.0 MPa and 0.8 MPa. Afterthe filtration, the dope 96 was transported and stored into a stainlessstock tank with volume of 2000 L while the temperature thereof wasregulated to 36° C. The stock tank comprised a stirrer which has ananchor blade on a central rotating shaft, so as to continuously stir thecontent in the stock tank. Further, no corrosion and the like happenedin portions of the devices for preparing the dope 96 from the lowconcentration dope, where the dope contacts.

In addition, a mixture solvent A including dichloromethane (86.5pts.mass), acetone (13 pts.mass) and 1-butanol (0.5 pts.mass) was made.

(1-4) Discharge, Casting, Bead Decompression

The film 141 was produced in the film producing apparatus 100 as shownin FIG. 9. The dope 96 in the reserve tank 90 was transported into thefiltration device 104 by a pump 103. The pump 103 has a function toboost a pressure in the primary side thereof. The pressure in theprimary side was controlled to 0.8 MPa by feedback for the upstream sideof the pump 103. The volume efficiency of the pump 15 was 99.2%. And thefluctuation of the volume of discharge was at most 0.5%. The pressure ofdischarge was 1.5 MPa. The dope 96 passed through the filtration device104 was transported to the casting die 110.

The casting die 110 to be used was 1.8 m in width. The casting was madewith regulating a flow rate of the dope from the casting die 110, suchthat the thickness of the produced film 141 might be 80 μm and the widthof the casting might be 1700 mm. In order to regulate the temperature ofthe dope 96 to 36° C., a jacket (not shown) is provided with the castingdie 110, and a heat transfer medium whose temperature was controlled to36° C. at an entrance of the jacket was fed into the jacket.

Temperature of the casting die 110 and pipes for was controlled to 36°C. while operating. The casting die 110 was coathanger type, in whichthe bolts (the heat bolts) for adjusting the thickness of the film wereprovided. Each pitch of bolts was 20 mm. The casting die 110automatically regulate the thickness of the film 141 by the heat bolts.The heat bolts preferably set the casting profile according to the flowvolume from the pump 103 by the preset program. The casting profile wasadjusted by the feedback control based on the measured value from theinfrared thickness measurement device (not shown) provided in the filmproduction device 100. Thus, in the film except of the edge portions,the difference of the thickness at any two points 50 mm apart ispreferably at most 1 μm, and further the difference of the minimalthickness value and the maximal thickness value in the widthwisedirection is preferably at most 3 μm. The adjustment was made such thatthe change of the film thickness might be reduced in the range of ±1.5%to the averaged film thickness.

In a primary side from the casting die 110, the decompression chamber120 was disposed, whose decompression value can be adjustable dependingon the casting speed, such that there would be a pressure difference inthe range of 1 Pa to 5000 Pa between up- and downstream sides from thebead (from the casting die to the casting belt 113). The pressuredifference was set such that the bead became predetermined length.Further, the temperature of the decompression chamber was also regulatedto be higher than a condensation temperature of the gas around thecasting bead. There was labyrinth packing (not shown) on the lips of thedie 110 in front and rear sides of the bead. Further, there wereopenings in both sides. Further, in order to compensate the disorder ofthe both edges of the casting beads, the edge suctioning device (notshown) was used.

(1-5) Casting Die

The material of the casting die 110 was the stainless havingdouble-phase structure. The material had coefficient of thermalexpansion of at most 2×10⁻⁵ (° C.⁻¹), the almost same anti-corrosionproperties as SUS316 in examination of corrosion in electrolyte aquasolution. Further, when the material was dipped in a mixture liquid ofdichloromethane, methanol and water, pitting (holes) were not formed onthe gas-liquid interface. The surface roughness Ry of a contactingsurface of the casting die 110 to the dope was at most 1 μm, astraightness was at most 1 μm/m in each direction, and the clearance ofthe slit was controlled to 1.5 mm. The end of the contacting portion ofeach lip to the dope was processed so as to have the chamfered radius atmost 50 μm through the slit. In the die, the shearing speed was in therange of 1 (1/sec) to 5000 (1/sec). On the lip ends of the casting die110, the hardened layer was formed by the tungsten carbide coating inthe spraying method.

On the both side edges of the die slit, the discharged dope is partiallydried to be a solid. In order to prevent the solidification of the dope,the mixture solvent A to which the dope was dissoluble was supplied at0.5 ml/min to each bead edge and the air-liquid interface of the slit.The pump for supplying the dope has a pulsation at most 5%. Further, thepressure in the rear side (or the upstream side) of the bead wasdecreased by 150 Pa. Further, in order to make the temperature in thedecompression chamber 120 constant, the jacket (not shown) was provided.Into the jacket, the heat transfer medium whose temperature wasregulated to 35° C. was fed. The airflow of the edge suctioning was inthe range of 1 L/min to 100 L/min, and in this embodiment, the air flowrate was regulated in the range of 30 L/min to 40 L/min.

(1-6) Material Support

The belt 113 was a stainless endless belt that was 2.1 m in width and 70m in length. The thickness of the belt 113 was 1.5 mm and the polishmentwas made such that a surface roughness was at most 0.05 μm. The materialwas SUS 316 and had enough corrosion resistance and strength. Thethickness unevenness of the belt 113 was at most 0.5%. The belt 113 wasrotated by drive of the two rollers 111,112. At this time, the tensionof the belt 113 was regulated to 1.5×10⁵ N/m², and the difference of therelative speed of the rollers 111,112 and the belt 113 was at most 0.01m/min. Further, the velocity fluctuation of the belt 113 was at most0.5%. The rotation was regulated with detecting the positions of bothedges such that the film meandering in width direction for one rotationmight be regulated to at most 1.5 mm. Further, the positionalfluctuation in the horizontal direction of the lips of the casting die110 and the belt 113 at just below the casting die 110 was at most 200μm. The belt 113 is provided in the casting chamber 115 with a device tocontrol the fluctuation of the airflow pressure (not shown).

Into the rollers 111, 112 are fed the heat transfer medium so as toperform the temperature regulation of the belt 113. Into the roller 111in a side of the casting die 110 was fed the heat transfer medium(liquid) at 5° C. and into the roller 112 was fed the heat transfermedium (liquid) at 40° C. The surface temperature of the middle portionof the belt 113 just before the casting was 15° C., and the temperaturedifference between both side edges was at most 6° C. Note that the belt113 preferably had no defect on surface, and especially preferably, thenumber of pinholes whose diameter was at least 30 μm was zero, that ofthe pinholes whose diameter was from 10 μm to 30 μm was at most 1 per 1m², and that of the pinholes whose diameter was less than 10 μm was atmost 2 per 1 m².

(1-7) Casting and Drying

The temperature of the casting chamber 115 was kept to 35° C. by thetemperature regulator 116. The dope is cast onto the belt 113 to formthe casting film 119, to which the drying air of parallel flow to thecasting film 119 was fed from the air blowers 121, 122 at first to dry.An overall coefficient of heat transfer between the drying air and thecasting film was 24 kcal/(m²·hr·° C.). The temperature of the drying airwas 135° C. in the upper and upstream side, 140° C. in the upper anddownstream side of the belt 113. And the temperature of the drying airfrom the air blower 123 was 65° C. in the lower side of the belt 113.The saturated temperature of each drying wind was about −8° C. Theoxygen concentration in the dry atmosphere was held at 5 volume %. Notethat the displacement of air to Nitrogen gas was made so as to keep thisoxygen concentration at 5 volume %. And in order to recover the solventin the casting chamber 75 by condensing, the condenser 117 was providedand the temperature at the exit of the casting chamber 115 was set to−10° C.

A wind shielding device 124 was provided in the casting chamber suchthat the drying air did not directly apply to the dope 96 and thecasting film 119 for five seconds from start of the casting, so as toreduce the fluctuation of the static pressure to at most ±1 Pa. When theratio of solvent in the solution casting film 119 reached to 50 mass. %(dry measure basis), the solution casting film 119 was peeled as the wetfilm 3 from the casting belt 113 supported by the peeling roller 125.Note that the content of the solvent (dry measure basis) was calculatedon a following formula:Content of Solvent={(x−y)/y}×100

-   x: weight of a sampling film before the drying-   y: weight of the sampling film after the drying    At this time, a tension on the wet film 3 was regulated to 1×10²    N/m², and the ratio of velocity of the peeling to that of the    running belt 113 was regulated in the range of 100.1% to 110%. The    surface temperature of the peeled film 3 was 15° C. An average speed    of the drying of the solvent in the casting film 119 on the casting    belt 113 was 60 mass. % (dry measure basis)/min. The solvent gas    generated in the drying was condensed and liquefied by the condenser    where a temperature was −10° C. and recovered by the recovering    device (not shown). Water content in the recovered solvent was    regulated to at most 0.5%. The dried air in which the solvent was    removed was heated again and reused as the drying air. The wet film    3 was transported into the tenter device 2 through the interval    section 130. In this transporting, the drying air (40° C.) was fed    to the wet film 3 from the air blower 131. Note that the    predetermined tension was applied to the wet film 3 while the wet    film 3 was transported by the rollers in the interval section 130.

(1-8) Transporting in Tenter Device, Drying, Slitting

The wet film 3 was transported through the tenter device 2 with the bothside edge portions of the film 3 were held by clips 10. In this time,the wet film 3 was dried by air. Then the dry air inside the dryingareas 2 a–2 c, which contains the vaporized TPP is send to the TPPremoving unit 65. The TPP removing unit 65 removes the TPP contained inthe dry air. The dry air in which the TPP is removed is fed to the freshair feeding pipe 55 connected to the TPP removing unit 65. In the freshair feeding pipe 55, outside air is taken from outside the pipe byopening the valve (not shown), and the outside air and the dry air fromthe TPP removing unit 65 flow together as the fresh air at the flow rateregulated by the valve 62. The fresh air through the fresh air feedingpipe 55 blows from the air outlets 56 provided in the first and secondclip covers 51,52 toward the clip 10, mainly toward the flapper 32. Afluctuation of velocity of the sprockets 11,12 were at most 0.5%. Thegaseous composition of the drying air was the same as that in thesaturated gas at the temperature of −10° C. An average speed of thedrying of the solvent in the wet film 3 in the tenter device 2 was 120mass. % (dry measure basis)/min. The condition in the drying zone wasregulated such that the content of the remaining solvent at the exit ofthe tenter device 2 was 7 mass. %. The wet film 3 was transported intenter device 2 with being stretched in the width direction B (see FIG.1). Note that when the width of the wet film 3 before being stretchedwas 100%, that of the stretched film 3 was 103%. The stretching ratio ofthe film from the peeling roller 125 to the entrance of the tenterdevice 2 was 102%. A ratio of the length between the position where theclips 10 started holding film and the position where the clips ended theholding, to the length between the entrance and the exit of the tenterdevice 2, was 90%.

The side edge portions of the film 141 were slit off by the edgeslitting device 142 within thirty seconds after exiting from the exit 17of the tenter device 2.

(1-9) Further Drying, Neutralization

The film 141 was dried at the high temperature in the drying chamber145. The drying air was fed in the drying chamber 145 such that insidethe chamber was partitioned into four partitions, and the respective airat 120, 130, 130 and 130° C. was fed into the respective partitionsarranged in an order from the upstream side to downstream side from airblowers (not shown). The tension of the film 141 given by the roller 144in the transporting was regulated to 100 N/m and the film 141 was driedfor ten minutes so that the content of the remaining solvent in the film141 finally became to 0.3 mass. %. A wrapping angle (arc of contact) ofthe roller 144 in winding the film 141 was 90° or 180°. The material ofthe roller 144 was aluminum or carbon steel, and the hard chrome coatingwas made on the surface of the roller 144. Two types of the rollers 144were used. In the first type, the surface of the roller was smooth, andin the second type, matting process is applied on the surface of theroller by blasting. The positional fluctuation (or eccentricity) of thefilm 141 on the rotating roller 144 was within 50 μm, and the deflectionof the roller 144 under 100 N/m tension was within 0.5 mm.

The solvent vapor in the drying air was removed by the adsorbing device146. The adsorbing agent was activated carbon, and the desorption wasperformed by the dried nitrogen. The water content in the recoveredsolvent was reduced to at most 0.3 mass. %, and thereafter the recoveredsolvent was used for the solvent for preparing the dope. The drying airincludes not only the solvent vapor but also the plasticizer, theUV-absorbing agent and the like having high boiling points. Thesecomponents were removed by cooling with use of a cooling device and apreadsorber, and recycled. The adsorption and desorption conditions wereset so that VOC (volatile organic compounds) in the exhaust gas mightbecome at most 10 ppm. An amount of the solvent recovered by thecondensing method was approximate 90 mass. % of all vapor solvent, andthe rest of the vapor solvent was mainly recovered by the adsorption.

The dried film 141 was transported into a first moisture controlchamber(not shown). The drying air at 110° C. was fed into an intervalsection between the drying chamber 145 and the first moisture controlchamber. The air with the temperature of 50° C. and the dew point of 20°C. was fed in the first moisture control chamber. Further, in order toreduce the generation of the curling, the film 141 was transported intoa second moisture control chamber (not shown). The air with thetemperature 90° C. and the humidity of 70% was directly fed onto thefilm 141 in the second moisture control chamber.

(1-10) Knurling, Winding Condition

The film 141 after the moisture thereof being controlled was cooled toequal to or less than 30° C., and both edge portions thereof were slitoff or trimmed by an edge slitting device (not shown). Theneutralization device (neutralization bar) 148 was provided so that thecharged voltage in the film 141 in transporting was kept in a range of−3 kV to +3 kV. Further, then knurling on the both sides of the film 141was made with use of the knurling roller 149. The knurling was givensuch that the film 141 was embossed from one of the both sides. Anaverage width of the area for knurling was 10 mm, and the pressure ofthe knurling roller 149 was determined so that an average height ofconvex might be 12 μm higher than the average thickness of the film 141.

Thereafter, the film 141 was transported into the winding chamber 150 inwhich the temperature and the humidity were kept to 28° C. and 70%.Further, an ionizer (not shown) was provided in the winding chamber 150so that the charged voltage in the film 141 was kept in a range of −1.5kV to +1.5 kV. The width of the product film 141 was 1475 mm. Thediameter of the winding shaft 151 in the winding chamber 150 was 169 mm.The tension of the film 141 was 300 N/m in the beginning of winding, andwas 200 N/m in the end of winding. The total length of the wound-up filmwas 3940 m. One length period of weaving measurement on the windingshaft 151 was 400 m, and a fluctuation range (oscillation range) in thewidth direction of the winding film was ±5 mm. The pressure of the pressroller 152 toward the winding shaft 151 was 50 N/m. In the winding, thetemperature of the film was 25° C., the water content was 1.4 mass, %,and the content of the remaining solvent was 0.3 mass. %. An averagespeed of the drying of the solvent in the film in the entire process was20 mass. % (dry measure basis)/min. There did not cause windinglooseness, creases and the like while the winding. Further, the windingdeviation did not cause in 10 G impact test. In addition, the appearanceof the film roll was in a good condition.

The film roll was stored in the storing rack where a temperature of 25°C. and a humidity of 55% RH (relative humidity) for one month. Then, thefilm roll was examined as same as the above described. According to theexamination, any significant change was not recognized. Further,adhesion of the film was not recognized in the film roll. Afterproducing the film 141, there was no remaining casting film 119 on thecasting belt 113. In addition, the TPP did not stick to the flapper 32and the dry bearing 37 of the clip 10 in the tenter device 2, and themass, formed by the binding between the particles on the dry bearing 37and the TPP, was not found. The flapper 32 could be rotated verysmoothly, and the wet film 3 was held by the clip 10 without fault.

In the above embodiment, the dry bearings 37 are incorporated in theflapper 32, the attachment shaft 35 is inserted to the holes 34 a of theflapper attaching portion 34 and the dry bearings 37, and then theattachment shaft 35 is fixed to the flapper attaching portion 34 by thefixing pins 36. However, the construction for attaching the flapper 32to the frame 31, with allowing the rotation of the flapper 32 around theattachment shaft 35 through the dry bearings 37, is not limited to thisembodiment. For example, the attachment shaft 35 may be fixed to theflapper 32, and the dry bearings 37 may be incorporated in the flapperattaching portion 34.

In the above embodiment, six of the fresh air feeding pipes 55 arerespectively connected to the portions of the first and second clipcovers 51,52 corresponding to each of the dry areas 2 a–2 c. However,the number of pipes 55 are not limited to this embodiment, as long asthe fresh air can be fed in the tenter device 2.

Although the present invention has been fully described by way of thepreferred embodiments thereof with reference to the accompanyingdrawings, various changes and modifications will be apparent to thosehaving skill in this field. Therefore, unless otherwise these changesand modifications depart from the scope of the present invention, theyshould be construed as included therein.

1. A tenter device used in a solution casting apparatus, said tenterdevice having clips for clipping both lateral edges of a film, andmoving said clips for transporting said film while dry air is fed from adry air blower onto said film for drying said film, said clipcomprising: a main body having a film holding surface on which saidlateral edge of said film is positioned; a holding lever swingablebetween a holding position for holding said lateral edge of said film onsaid film holding surface and a retreat position for releasing saidholding of said film; an attaching shaft for attaching said holdinglever to said main body; at least one dry bearing supporting saidattaching shaft, said dry bearing being formed of material whichgenerates lower dust by wearing compared to material containing lead andis self-lubricating; a clip cover for covering a moving path of saidclip in the state that said holding lever is at said holding position;and a fresh air blower for feeding fresh air into inside of said clipcover so as to prevent said dry air outside of said clip cover fromblowing into inside of said clip cover.
 2. A tenter device described inclaim 1, wherein said dry bearing contains polytetrafluoroethylene andsolid lubricant.